The present invention pertains generally to telephone common control switching systems and specifically to the dial pulse receiving equipment contained therein.
When a telephone call is placed from one telephone exchange to another, the latter must be capable of receiving and processing the dial pulse information irrespective of the dialing speed of the caller (now greatly enhanced by Touch Tone.RTM. calling). In modern common control switching systems, this is accomplished by providing therein storage equipment for receiving and storing locally the dial pulse information generated by a local calling subscriber until a signal, such as a "wink start", is received from the foreign exchange serving the called subscriber indicating that a selected register in the foreign exchange is ready to receive the information.
When the calling exchange is of the older electromechanical type, such as a step-by-step system, a problem arises in that there is no capability provided for storing the information, so that the dial pulses are transmitted immediately upon generation by the calling party or exchange whether or not the called exchange has had sufficient time to assign and connect a register to receive the pulses.
Prior art common control switching systems overcome the foregoing problem through by-link circuits which are associated with the trunks connecting the switching systems to electromechanical systems and which are operated by the common control processor serving the switching system to expeditiously effect a direct connection from the trunk to a register, thereby bypassing the network and avoiding the delay (and possibly loss of dial pulse information) ensuing from the normal connection via the network as when the call is from another common control switching system. Aside from the additional by-link circuit equipment this arrangement requires, the common control processor is taxed by interrupting numerous other functions to perform the function of controlling that circuit when calls are received from the older electromechanical systems.
Accordingly, with the foregoing in mind, it is a primary object of the present invention to provide a method and apparatus for delaying the dial pulse information for a time sufficient to establish a trunk to register connection.
It is a related object of the present invention to delay dial pulse information by storing the information temporarily within the trunk circuit itself.
It is a further object of the present invention to provide an economical dial pulse storage circuit for use in telephone trunk circuits having both immediate start and delay dial capabilities.
It is a feature of the present invention to provide an n-bit wide random access memory for the delay-storage element, whereby such memory serves to delay dial pulse information for n number of trunk circuits.
It is a further feature of the present invention to provide a trunk circuit which automatically inserts a guard band time period before recognizing electrical transitions on the trunk line as dial pulses, when operating in the delay dial mode.
The foregoing objects as well as others, and means by which they are achieved through the present invention, may be best appreciated by referring to the detailed description which follows hereinafter together with the appended drawings.